All but 1 of the 5 Mexican Gray Wolves released in Sonora in October of 2011 have been poisoned to death by warfarin, which is commonly used by ranchers and others to kill mammals. The wolves were found dead in Nov. and Dec. of 2011. Although uncertain, there is a good likelyhood that this is a targeted killing of the wolves. It takes high levels of warfarin to kill large mammals.
One of the wolves is alive and doing well. Mexican officials have said they will continue with the program although no details on further releases have been given.